To assess respiratory symptoms, USC scientists studied children in eight California communities and defined bronchitic symptoms over the preceding year as a daily cough for at least three consecutive months, congestion or phlegm not related to a cold, or inflammation of the mucous membranes, according to Kiros Berhane, lead author and a professor of preventive medicine at the Keck School of Medicine of USC.
The study, published April 12 in the Journal of the American Medical Association, followed 4,602 children in three cohorts as they aged from 5 to 18. During 1993 to 2012, children and their parents from Long Beach, San Dimas, Upland, Riverside, Mira Loma, Lake Elsinore, Alpine and Santa Maria answered questionnaires about children's health. Air quality was continuously monitored in each community.
The study found that tiny particles called particulate matter 2.5 (PM 2.5) -- which can penetrate deep into lungs and cause serious health problems -- dropped by 47 percent from 1992 to 2011 in the study region. USC researchers were able to associate cleaner air with improved children's respiratory health. Kids with asthma were 32 percent less likely to suffer from bronchitic symptoms, and children without asthma experienced a 21 percent reduction in these respiratory problems.
Moreover, nitrogen dioxide, which can reduce resistance to respiratory infections, decreased by 49 percent in the same two decades. USC researchers linked the drop in nitrogen dioxide with a 21 percent decrease of bronchitic symptoms in children with asthma and a 16 percent decline of bronchitic symptoms in kids without asthma.
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